Or instead of this, actually put an effective vetting system in place for drivers. That would not require super-strict privacy control and the inevitable hack. (having this data would make uber the most juicy target for spy agencies)
There is no vetting system that can separate criminals from "normal people", beyond looking at obvious stuff like past convictions. Sex offenders don't look or act any different than the rest of us.
Given Uber's history, this feature is almost certainly not "for the good of the consumer". Audio data has a lot of value these days, and I imagine Uber has a lot to gain from having a large trove of it.
Why would this data be so valuable? In an Uber people are with a stranger in their car so they will probably not have super confidential conversations.